Recovery of resins from coal



fatented May 2, 19 i RECOVERY OF RESINS FROM COAL Ernest Klepetko and Philip de B. Kaye, Bauer,

and Lester J. Hartzell, Jr., Tooele, Utah, assignors to Combined Metals Reduction Company, Stockton, Utah, a corporation of Utah No Drawing. Application J une 17; 1946 Serial No. 677,394

8 Claims. (Cl. 260-107) 'Thisinvention relates to the recovery of resins from coal, and is particularly directed to the production of a resin concentrate by flotation from resin-bearing coal. The invention has for its principal objects to produce a resin flotation concentrate which is easily amenable to further refining (as by solvent extraction), and to produce a salable coal residue. These objects are achieved in accordance with the complete process of the invention by controlled crushing of the coal preparatory to flotation, by proper control of the pulp density of the c-oal-bearingpulp during nomically and on a commercial scale has presented serious difficulties. In United States Patent No. 1,773,997, granted August 26, 1930, to William D. Green, it is pointed out that solvent extraction of the resin directly from the coal is wasteful of the solvent, and that separation by means of a liquid of high specific gravity is accompanied by substantial mechanical loss of the liquid used and contamination of the products. Sink-and-float, processes more recently proposed are not effective for adequate and efficient recovery of the finer resin particles. Green proposed separating the resin by a flotation process, using one of the high alcohols, turpentine, cresol, one of the pine oils, or the like, as the flotation agent.

. Greens process is effective for producinga flotation concentrate containing a high percentage of resin, but the resin concentrate is not sufflciently pure for most commercial uses without further refining. Refining by solvent extraction isparticularly desirable, because the resin is unaifected by the solvent extraction treatment, and when a resin flotation concentrate is used as the raw material in a cyclic solvent extraction process, the consumption of solvent is economi-- cally low. Practically, however, solvent extraction refining of a resin flotation concentrate produced in accordance with Green's method is very difiicult, because the insoluble coal contaminants in the resin concentrate are so fine that they cannot be separated economically and efiiciently from a solution of the resin in a solvent. Although this insoluble matter constitutes only a small percentage by weight of the concentrate, it is present in such a fine state of comminution that it will not settle on standing, and quickly plugs up the pores of any satisfactory commercial filter medium.

In the course of an exhaustive investigation of this problem, we have determined that the resin is far more friable than the coal with which it is admixed. In addition, careful examination of numerous coal samples from a number of mines has disclosed that the resin occurs in fracture planes of various thicknesses, and that the finest resin grains in these planes ordinarily are oiabout 40-mesh size. Our investigations have revealed. that, owing to the friability of the resin and the consequent tendency of the coal to fracture along the resin seams, and to the fact that the resin particles in the coal are not excessively fine, substantially all of the resin is liberated from its. mechanical bond to the coal if the coal is crushed only enough to pass a 6-mesh to S-mesh screen.- We have further discovered that the excessively fine character of the coal impurity present in resin concentrates as heretofore prepared by the Green flotation process is due to unnecessarily fine crushing of the coal preparatory to flotation, and to comminution that occurs by attrition during the course of the flotation operation.

Based on these discoveries, our present invention contemplates crushing the resin-bearing coal no finer than necessary to pass a 6- to 8-mesh screen, and forming a pulp of the crushed product,

in water. The density of the pulp is adjusted to not more than about 15% by weight of solids, and the resulting pulp is subjected to a flotation; operation in an air agitated flotation unit in the absence of mechanical agitation. The coarse crushing of the coal is adequate to liberate the resin sufliciently for effective flotation, but pro-.

duces a minimum-of fines. Maintaining the pulp density at a low value, below about 15% solids, facilitates settling of such coal fines as are pro'-:

duced and so tends to keep them out of the floated trate. When used in combination, these features permit of producing a resin concentrate having a screen analysis approximating at least about plus IOU-mesh, and in which the contami- Thus the foregoing features each contribute to avoiding formation of. coal fines and to preventing accumulation of this objectionable impurity in the resin concen-jnating particles of coal are therefore sufiicientlycoarse tobe readily amenable to removal. during.

refining of the concentrate by solvent extraction, which involves dissolving the resin from the con-- centrate in a solvent for the resin-and then sep,a-, rating the insoluble coal residue from the'solution by filtration, thickening, or. otherwise.

The fact that relatively coarse'cr-ushingis ade: quate to liberate the resin sufficiently for substantially complete recovery by flotation was demonstrated by tests conducted on three large, batches of coal all obtained from the same source One batch was reduced by carefully controlled crushing to pass through a ZO-mesh screen, a second bath was carefully crushed to passa 1 mesh screen, and the third batch was reduced by equally careful crushing to pass onlya G-mesh screen. Each batch was separately-subjected to a" flotation operation using pine oil as the flotation agent. Practically identicalresinrecoveries were obtained in the flotation concentrate from each batch. Hence it is evident-thatcrushing to the finer sizes is not necessaryto; secure improved resin recoveries inthe flotationconcentr ate. The physicalquality of the concentrates produced from the more coarsely crushed batches of coal was decidedly superior to that of the concentrate obtained from the batch crushed to minus 20-mesh.- Moreover, the coal tailing from themore coarsely crushed batches contained a a substantially lower-percentage of-fines than did the tailing from the ZO-mesh material, and consequently was a much morereadily salable coalpr'oduct.

' These tests establish that crushingno finer than necessary to pass a 6-or-8-mesh-screen is ample for-obtaininga high resin recovery in the flotation concentrate, and leads to the production of-a resin concentrate and a coal-tailing having phys-' ical properties superiorto what can-be-obtained when the-raw material-is crushed to the finer sizes heretofore customary in such flotation operations.

The pronounced effect of attrition in producingfinesin. the course of the flotation operation is demonstrated by the data set forth in Table I. These-data were obtained from screen analyses onthe solids contained in the .feed to a resin flotationoperation, and in the tailing and concentrate-products. The resin-bearing coal feed was prepared. 'for this operation by controlled graded crushing of a large'lot to a 8-mesh size, aridtheflotation operation was carried out in a standard. commercial-size. mechanically agitatedflotation machine. The screen analysesset forth inethe last three columns are expressed in percent solids ofthe screen size indicated in-the first column.

Theexcessive attrition which occurred during the flotation operation is well shown by the foresoingscreen analyses. Forv example, it will be noted that whereas the original feed contained only 16.9% minus IOU-mesh, the coal tailing contained almost four times as much (62.1%) minus lee-mesh material, and that the concentrate was aimostall (93.7%) minus lOO-mesh.

The "screen analyses reported in Table I are based on a flotation operation conducted in a mechanically agitated flotation unit. We have found that the attrition and production of fines that occurs during the flotation operation may be greatly reduced if the flotation is conducted in an air-agitated unit. such air-agitated flotation units are exemplified by the Callow canvas bottom-cell, the McIntosh cell with canvas cover air rotor, and the air-lift Forrester type of cell. In general, using the; coarsely crushed feed that weprefer to employ, the air-lift type of flotation machine is generally mostsatisfactory.

In order to compare the attrition characteristicsof mechanically agitated flotation units with those ofair-agitated flotation units, a batch of coal carefully crushed to pass a ZO-mesh screenwas subjected to a flotation operation in an airlifttype of cell, and another batch of coal carefully crushed to pass an S-mesh screen was subjectedto a flotation operation in a mechanically agitated cell. The screen analyses obtained for the feed and concentrate in each of these operationsis set forth in Table II. Again thescreen analyses are expressed in percent solids of the screen size shown in the first column.

TABLE II Attrition. characteristics of. mechanically agitated and air-lift. flotation units.

Feed Concrentrate Mesh Mechan. Air-Lit t Mechan; Air-Lift- Per Cent Per Cent Per Cent Per Cent Cumu- Oumu- Cumu- Cumu-.

lative lative lative lative' The screen analyses reported in Table 1 1- Show how-much greater is the amount ofattrition thatoccurs in themechanically agitated cell-than in the air-agitated type of cell. In spite of the fact that the air-lift cell was operated on *a' very-much finer-feedtharrthe mechanically agitated- 'cell,-- thus favoringthe latter; the concen'-- trate obtained fromtheair-Iii t machine contain'ed only 54.4% minus l-OO-meshwhereasthe concentrate fromthe mechanical-1yagitated-cellcontained- 93.7% minus IOU-mesh The mugh coarser concentrate obtained using j the air liit cell inthe absenceof-mechanical agitation (the screen analysis of which-concentrate approximated- 50% plus -mesh was" considerably more amenable to refinement lay-solvent extrac tion than was-the relatively finer concentrate 'ob1-' tamed-from the mechanically agitatedunit-P In addition, the coal tailing produced in theairlift cell-was coarser and moreireadily salable than was the coal tailing produced in'the mechanically agitated cell.

Asa matter of interest-,the screen analyses set forthin Table II areindicative 'offhow readily friable is the resin contained in the coal; Even in the case of the air-lift type of machine, with its gentle agitation of the pulp, the screen analysis shows that whereas only 20.7% of the feed (mostly coal) was minus 100-mesh, over 2% times this amount of the concentrate (mostly resin) was minus 100-mesh. Table I also indicates the friable nature of the resin, in that it shows the much coarser quality of the coal tailing as compared with the resin concentrate from the same flotation unit.

A further important factor which affects the quality of the resin concentrate is the density of the pulp in the flotation circuits. This pulp consists of a water suspension of the solid coal and resin particles, in which the solid particles are in a constant state of random motion induced by agitation and by flow of the pulp. The random motion of the solid particles in the pulp results in frequent collisions between the particles, with consequent attrition and production of fines. The frequency with which collisions occur, and hence the amount of fines produced in this fashion, is to some extent a functionof the pulp density. A low pulp density favors avoiding the production of fines. While it is not possible to set a hard and fast maximum limit of pulp density, we have found that, in general, the most satisfactory concentrate for subsequent refining by solvent extraction is obtained if the maximum pulp density employed in the flotation circuit does not exceed about 15% by weight of solids.

The flotation operation may be conducted in two or more steps, employing rougher and cleaner flotation operations. In the rougher operation a coal tailing low in resin content, and a resin middling, are produced. In the cleaner operation, the resin middling from the rougher operation is floated under conditions designed to produce a resin concentrate containing a minimum amount of coal impurities, and a tailing consisting of a mixture of coal and resin which may be returned to the rougher operation for retreatment. The .cleaner operation may in turn be conducted in two or more separate cleaner flotation steps to secure production of a high grade resin concentrate.

When conducting the flotation operation in two or more steps as outlined above, it is generally most advantageous to maintain the pulp density in the rougher circuit at a value not above about 15 solids and to conduct the cleaner operations at considerably lower pulp densities. For example, in a three-step flotation operation, employing two cleaner stages, the pulp density in the first cleaner stage advantageously does not exceed about 10% by weight of solids, and it is best if the pulp density in the flnal cleaner stage does not exceed about 8% by weight of solids.

While a low pulp density promotes production of a clean concentrate free from an objectionably high quantity of fines, commercially eflicient conduct of the flotation operation sets practical minimum limits to the pulp densities. If the pulp densities are too low, excessively large volumes of pulp have to be handled, and a large plant is required in relation to the amount of resin concentrate produced. By way of example, advantageous and practical pulp density limits in the several stages of a three-step flotation operation of the character outlined above are about 10% to about 15% by Weight of solids in the rougher stage, not over about 10% and not less than about 5% by weight Of solids in the first cleaner stage, and not over about 8% and not less than about 3% by weight of solids in the final cleaner stage.

The total amount of fines appearing in the concentrate (and in the coal tailing) produced in a. given flotation unit depends, of course, on the amount of coal slime made in preparing the feed to the first flotation unit, as well as on the pulp densities prevailing during flotation. To some extent, therefore, the optimum pulp density to be employed will be governed, in part at least by the amount of fines initially present in the flotation feed.

Control of the factors that influence fine productionis important not only for the purposes of producing a coarse coal tailing and a resin concentrate in which the coal impurities are sumciently coarse to be readily separated in a refining process, but also to minimize the extent to which coal impurities accumulate in the resin concentratethat is, to produce a clean concentrate. Due to the low specific gravity of the coal in the pulp, there is always a tendency for very fine coal particles to float over with the resin concentrate. The greater the amount of coal fines present in the flotation pulp, the greater will be the proportion of coal impurities that find their way into the resin concentrate, assuming other conditions remain constant. sity is a particularly important factor in this connection, as such control not only aids in minimizing the production of fines by attrition, but is of material consequence in minimizing the tendency of such coal fines as are formed to float with the resin concentrate. For this purpose, the pulp density should at all times be sufliciently low so that substantially free and unhindered settling. of the coal particles can occur. It is chiefly for this reason that the pulp density in the cleancrcircuits of a multi-stage flotation operation should be considerably lower than in the rougher circuit. The resin middling product which constitutes the feed to the cleaner operations is com-- posed of a much higher proportion of fine material than is the feed to the rougher operation, and the fine coal particles in this product settle less readily than do the coarse coal particles in the rougher pulp. Accordingly a more dilute pulp is necessary in the cleaner stages than in the rougher stage in order to favor settling of the coal fines and so reduce their tendency to float over with the cleaner resin concentrate. With a pulp of properly low density, separation of the coal fines and resin is also favored by the difference in specific gravity between the coal and resin (the specific gravity of the coal ordinarily is about 1.6 and 0f the resin about 1.2). We have found that pulp densities within the limits set forth above are generally satisfactory for producing a resin concentrate of good commercial quality and low in undesirable coal impurities.

In contrast to accepted procedures for floating sulphide minerals, and in contrast to floation practice as sometimes employed in coal preparation, it has been found that the resin can be floated to the surface of the pulp without the use of air. However, air introduced into the pulp is a. desirable accelerant for bringing the resin to the surface, and accordingly, it is advantageous to conduct the flotation operation in an air-agitated unit in order to secure rapid collection of the. resin concentrate. The air admitted to the pulp.. especially in a cleaner operation, should not enter so rapidly as to cause a degree of agitation too great to permit fairly ready settling of the coat Proper control of the pulp denfines,- for otherwise, as indicated above; it will be difiicult to produce a clean resinconcentrate.

-We=have-found that a very goodgr'ade of resin concentrate,- and areadily salable coal tailing, may be produced in the course of a flotation operation conducted as herein described. The coal tailing-is coarser, and so generally more acceptabIe to-the trade, than has been produced by heretofore known flotation methods for recov ei-ingresinsf om coal. A goocl recovery of resin inthe concentrateis attained, and the concentrate is high in resin content and of excellent physical characteristics for subsequent refining by solv ent extraction or otherwise. While it is not:-generally economic to degrade coarse coal, such'as nut or lump coal, by crushing merely to lib'e'rateand recover its resin content, the 'fiotation method herein described may be applied economically to the coal screenings. dition to recovering the resin as a valuable by-' In adseparating-the-resulting resin solution from the insoluble-constituents of the concentrate, theimprovement which comprises crushing the resinbearin'g -coalno finer than no essaryto' pass a 6-.-:-1to' 8-rneshscreen and forming a pulp of the" crushed pr oduct inwat'er, adjusting the density of th'e pulp to no more than aboutie /b weight ofi-soli'ds, and subjecting the resulting pulp toi the -flotation'operation in an air-ag itatedfiota= tion-unit and in the absence-of mechanical agitat-ion ofssthe pulp, whereby: when the resin. con

centrate is leached"; the resin solution thereby obtainedis readily'separated by filtration :Erorrr theiinsolubleconstituents of the concentrate.

' 2;; nila-processfor the recovery of a resin from" resin-bearing coal involving crushing the coal,

suhiecting the crushedcoal to a flotation opera tionrto prepare-laresin concentrate, leaching the: concentratevwith a-solvent'for the resin, and

searating. the resultingresin solutioniroin the insoluble constituents of the. concentrate, theimprovement which comprises crushingthe resin-- bearinglcoal no-finerfithan necessary to pass a 6-.'to.-8U-rnesh screen. and forming a puip of the crushedproduct Water, adjusting the density of; the pulp to' no more than about 15% by weightlof-solids, subjecting the resulting pulp to a rougher flotation operation in an-air-agitated' flotationv unit and in the absence of mechanical agitation of the pulp, separating and recovering the rougher coal tailing, separating therougher' resin concentrate product and incorporating it in a pulg' 'having a density no greater than about 10% 'byweightof solids, and'subjecting the resultingpulp to a cleaner flo-tation'o oerationin a second' air-agitated flotation unit and in the ab sence of mechanical agitation, whereby when the resin concentrate leached the resin solution therebyobtained is readily separatedby filtra--' tion-irom the insolubleconstituents of the concentrate.

3-. In a process for-the recovery of a resin fromresin bearing coal -involvingcrushing the coal, subjectingthe crushed coal to a flotation operatioxi' to prepare a resin concentrate, leaching the attests 8 concentf' tswruia se1teritreta mating th resumesre'siii sol" soluble'cons'tituents' of the co.

' when they resin concentrate is lcachedthe}itlnfesfin solution thereby obtained is readfly senfated by-filtration iro'n'ithe' insoluble -constituentsof" the'conce'ntrate; g Y

xIn a processior the recovery of a resin a resin-bearing "coal-1 involvingsubject'in'g a-pulp' containing the resin-hearing co'alto rcugher'afict cleaner flotation operations to prepare a re concentrate and leaching said concentrate 'wit solvent-for the resin, the improvement wfn comprises-"maintaining the polio density in 'the' rougherfiotatio'n operational; a value no higher than about 15% by weight of solids, and maintaining the pulp density in the cleaner flotation; operation at" a value, no higher than aboutl0% 31 by weight of solids, whereby when theresinf'conq centrate is leached the resin: solution thereby obtained isreadily separated by filtration ham" the insoluble constituents" of. the concentrate.

5.1 In aprocessicr therec'o've'ry'oi' a resin f a re'Sih-bcarihicoal involving'crushing the coal; subjecting the crushed coal to a flotation o eration/to prepare a resin concentraTta leachingthe concentrate with a solvent for the resin, and' se arating the resulting resin-solution from the insoluble:constituentsof the concentrate, the improvement which comprises conductingthe fio ta tionin an air-agitated flotation-unitin the ab senceof mechanical agitation, whereby when the" resin-concentrate, is leached theresin" solutionthereby obtainedis readily separated by filtrationr-from the insoluble constituents-of the-conecentrate.-;-

6. in a vprocess'for the recoveryof a resin from" f a resin-sbearing, coal,- involvingcrushingthe-coalf suhiecting the crushed coal" to a flotation opera--- subfje'cting th'e' crushecl -coa hto a fiotationopei'a tion-to l prepare a resin concentrate, leaching the 1 concentratewith a sol-vent for the 'resih', and-' separating theres'ultihgfresin solution from-the insoluble constituents of the concentrate; the m prtive'm'ent' which'cornprises crushing the coal no rnore than-necessary to enable the crushed prod uct"topassa 6'-rnesh screen prior tosubj'ectihg" it 'to the fiotation operation' to hro'ducathe'. resinr: concentrate; 5 whereby a when the concentrate. isf leachedtheresin solution thereby obtained is readily-separated by filtration from the insoluble constituents Qf th'e concentrate.

8; The improvement according to claim' 5, characterized in that the pulp densityfiduringi the:

0 flotation operation is no greater than about 10% OTHER REFERENCES by weight of solids.

Gaudin, F1otation," 1932, McGraw Hill 00.,

ERNEST KLEPETKO. PHILIP B, KAYE 117, 118, 120, 121, 122, 131, 139, 140, 142,

LESTER H EI JR 5 143, 151, 152, 153, 154, 350 to 353.

American Institute of Mining and Metallurgi- REFERENCES CITED cal Engineer, Contribution No. 86, copyright 1935, pages 3, 4, 5, 6. g 3. gg g i are of record in the Denver Equipment Index, 1936, Denver Equip- 19 ment 00., Denver, (3010., pages 104, 105. UNITED STATES PATENTS Bureau of Mines Report of Investigations, No. Number Name Date 3599, 1941, pp. 16.

1,773,997 Green 1. Aug. 26, 1930 Nagelvoort, Chemical and Metallurgical En- 2,364,090 Nagelvoort Dec. 5, 1944 gineering, Oct. 1942, pp. 80-82. 

7. IN A PROCESS FOR THE RECOVERY OF A RESIN FROM A RESIN-BEARING COAL, INVOLVING CRUSHING THE COAL, SUBJECTING THE CRUSHED COAL TO A FLOTATION OPERATION TO PREPARE A RESIN CONCENTRATE, LEACHING THE CONCENTRATE WITH A SOLVENT FOR THE RESIN, AND SEPARATING THE RESULTING RESIN SOLUTION FROM THE INSOLUBLE CONSTITUENTS OF THE CONCENTRATE, THE IMPROVEMENT WHICH COMPRISES CRUSHING THE COAL NO MORE THAN NECESSARY TO ENABLE THE CRUSHED PRODDUCT TO PASS A 6-MESH SCREEN PRIOR TO SUBJECTING IT TO THE FLOTATION OPERATION TO PRODUCE THE RESIN CONCENTRATE, WHEREBY WHEN THE CONCENTRATE IS LEACHED THE RESIN SOLUTION THEREBY OBTAINED IS READILY SEPARATED FILTRATION FROM THE INSOLUBLE CONSTITUENTS OF THE CONCENTRATE. 